Heretofore, in projector type image display devices, halogen lamps have been used as light sources. However, in recent years, since light sources using laser diodes have been developed, devices in which these laser diodes are used as light sources have come into practical use. In such an image display device, very straight light (laser beam), which is emitted from a light source, is modulated in order to represent gradation, and the modulated laser beam is projected on a screen to display an image. In order to project a two-dimensional image using such an image display device, the light from the light source must be scanned by some method. There is one such method in which the laser beam is raster scanned using scanning mirrors such as MEMS (Micro Electro Mechanical Systems) mirrors.
In a laser printer or a copying machine also, a laser diode is used as a light source in order to write an image using a laser beam. The laser beam emitted from the laser diode is scanned by a scanning mirror such as a polygon mirror or a galvano mirror.
For such a scanning mirror, a resonant oscillation type mirror is used in which mechanical resonance is used for high speed scanning. The shear modulus of elasticity (modulus of transverse elasticity) of a hinge section which supports this resonant oscillation type mirror has temperature characteristics. Therefore, the resonant frequency of the resonant oscillation type has characteristics that vary as the temperature changes. As a result, even if the resonant oscillation type mirror is driven at a constant frequency, there is a problem in that the oscillation angle of the oscillation, and the phase difference between the phase of the oscillation and the phase of a driving signal, vary as the temperature changes. Furthermore, since the restoring force of the hinge section increases as the oscillation angle of the mirror becomes greater, there is also a problem in that the resonant frequency fluctuates due to the oscillation angle.
In order to correct these problems, a method is used in which control is performed while detecting the oscillation angle of the scanning mirror. For such a control method, a method is disclosed in Patent Document 1 for example, in which a light receiving unit is provided at one end, outside of the effective scanning range, and the oscillation angle is controlled by detecting the timing at the light receiving unit. Moreover, in Patent Document 2, a method is disclosed in which separate light receiving elements are arranged at the top, bottom, right, and left sides of a screen on which a projector projects an image, and the amplitude is controlled by the detection results of the separate light receiving elements.